The present invention relates to novel methods for preparing quinoline-2,3-dicarboxylic acids. These acids are useful intermediates in the preparation of herbicidal pyridine and quinoline imidazolinone herbicidal compounds.
The herbicidal pyridine and quinoline imidazolinone compounds prepared from the present compounds include 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)quinoline-3-carboxylic acid, esters and salts thereof and are disclosed in European Patent Application No. 0 041 623, (incorporated herein by reference). These herbicidal imidazolinyl quinolinecarboxylic acids may be prepared by the procedure described in U.S. Pat. No. 4,518,780 (incorporated herein by reference) by cyclization, under basic conditions, an appropriately substituted 2-carbamoyl quinoline-3-carboxylic acid that, in turn, is prepared by the reaction of a substituted quinoline-2,3-dicarboxylic acid anhydride and appropriately substituted aminocarboxamide or aminothiocarboxamide. Quinoline-2,3-dicarboxylic acid anhydrides are prepared from the diacids by procedures well known in the art. However, the diacids themselves are not readily available.
Pending application for U.S. patent of Robert Doehner, Ser. No. 698,192 filed Feb. 4, 1985 (incorporated by reference) describes a method useful for the preparation of quinoline-2,3-dicarboxylic acid and esters thereof by reacting a beta-anilino-alpha,beta-unsaturated ester with an immonium salt (commonly called a Vilsmeier reagent). The beta-anilino-alpha,beta-unsaturated esters are obtained by the reaction of appropriately substituted anilines with keto-esters or dialkyl acetylene dicarboxylates. This overall reaction for the preparation of quinoline-2,3-dicarboxylates is illustrated in Flow Diagram I. ##STR1## wherein R' is CH.sub.3 or CO.sub.2 R" and R" is C.sub.1 -C.sub.4 alkyl and R"' is CH.sub.3 (or C.sub.1 -C.sub.4 alkyl).
When R' is CH.sub.3, the diacid is obtained by concurrent oxidation and hydrolysis of the product under aqueous basic conditions in the presence of nickel peroxide as described in U.S. Pat. No. 4,459,409 (incorporated herein by reference).
Unfortunately, the availability of ketoesters and dialkyl acetylene dicarboxylates, such as diethyloxalacetate and diethyl acetylenedicarboxylate, is limited, thus restricting the quantities of anilino-fumarate and quinoline-2,3-dicarboxylic acid, the intermediate required for preparing herbicidal 2-(4-isopropyl-4 -methyl-5-oxo-2-imidazolin-2-yl)quinoline-3-carboxylic acid, esters and salts thereof.